1. Field of the Invention
This invention relates to vacuum cleaner bags having at least two layers and wherein the inner layer is comprised of a non-woven air filter formed of melt-blown, microfiber webbing.
2. Description of the Prior Art
A variety of vacuum cleaner filters utilizing non-woven components are known. For example, U.S. Pat. No. 2,813,596 discloses a disposable vacuum cleaner dust container that has a strong, porous wrapper of sheet material able to filter dust particles from an air stream and a liner that includes plies of creped, cellulosic wadding.
U.S. Pat. No. 3,498,031 relates to a vacuum cleaner bag containing a reinforcing and auxiliary filter insert of felt-like material and U.S. Pat. No. 4,540,625 is concerned with a flexible composite useful in fabricating filters and having a fiber mass of a randomly oriented mixture of non-woven substrate fibers and organic polymer fibers intertwined therewith and containing solid sorptive microscopic particles disposed against the non-woven fibers to form a flexible, air permeable, absorbent fiber filter. Other examples of filters using non-woven components will be found in U.S. Pat. Nos. 3,535,855, 4,257,791 which is a division of U.S. Pat. No. 4,164,400, 4,397,907 and 4,522,876.
Of particular interest is U.S. Pat. No. 4,589,894 which explains that vacuum cleaners typically draw air at relatively high velocity and volume adjacent a surface to be cleaned to pick up loose dirt and debris. They then expel an air stream which includes the dirt and debris through an outlet fitted with an air filter which separates the dirt and debris from the air stream.
It is also explained that the selection of materials which form the filter is somewhat limited inasmuch as the filter must be sufficiently strong to withstand the pressure build up in the vacuum cleaner yet have a porosity which permits the passage of air at a sufficient rate while filtering the dust and debris.
The patent cites the Ninth Technical Symposium: "Nonwovens in the '80s: Years of Change" March 9, 1981 sponsored by INDA Association of the Nonwoven Fabrics Industry, for its teaching that melt-blown polypropylene micro-fiber webs would provide a superior filter as compared to paper with respect to dust pickup and yet have a low pressure drop. It points out, however, that such filters are known to be relatively fragile and will not, without rupture, sustain the pressure build up caused by a vacuum cleaner. It goes on to say that such filters have insufficient strength to resist damage induced by mechanical erosion caused by the influx of airborne dirt and debris or sufficient tensile strength to resist tearing because of sagging as the bottom of the bag fills with dirt. Further, the '894 patent reports that micro-film webs are known to be very susceptible to damage just in handling and therefore are thought to be unlikely candidates for use in vacuum cleaners where handling to permit filter placement is a must.
U.S. Pat. No. 4,589,894 also refers to several patents including U.S. Pat. No. 4,116,648 for its disclosure of a disposable vacuum cleaner filter bag made with a relatively weak but efficient fiberglass filter spaced between support layers of air pervious paper. The '894 patent notes however, that such a construction would not be suited for use with the micro-fiber web since the paper support members would act as a paper filter and would typically clog early, drastically reducing the useful life of the filter.
With the foregoing considerations in mind, U.S. Pat. No. 4,589,894 discloses a vacuum cleaner disposable filter, preferably in the form of a closed container, having an inlet for connection to the air discharge outlet of a vacuum cleaner and comprising an assembly of layers. The inner filter layer of that assembly is provided by a non-woven micro-fiber web formed of randomly entangled synthetic polymer micro-fibers sandwiched between highly porous outer support layers each preferably comprising spun-bonded, non-woven webs on either side of the inner layer
More specifically, that patent teaches a filter comprising an assembly of juxtaposed layers, as follows: (a) a first outer support layer of highly porous fabric formed of synthetic fibers, the fabric having an air permeability of at least 100 m.sup.3 /min/m.sup.2 and a grab strength of at least about 1.0 kg; (b) an inner filter layer formed of a web comprising randomly interentangled synthetic polymeric microfibers that are less than 10 microns in diameter and having a weight of about 40 to 200 g/m.sup.2 and an air permeability of about 3 to 60 m.sup.3 /min/m.sup.2 ; and (c) a second outer support layer of highly porous fabric formed of synthetic fibers, the second outer support layer being disposed on the opposite side of said web from the first outer support layer, the fabric of the second layer having an air permeability of at least 50 m.sup.3 /min/m.sup.2 and a grab strength of at least about 1.0 kg.
The outer support layers preferably are highly porous and light weight webs of synthetic fibers which are spun bonded, spun laced, bonded wet laid, or net-like fabrics.